This invention relates to a method for sorting radioactive waste having a low level of radioactivity and more particularly to a method which is inexpensive and efficient.
The waste presents problems due to the danger of injury to those that may come into contact with it notwithstanding the fact that only low levels of radioactivity are present. Thus, while it is generally acknowledged that exposure to low levels of radiation over long periods of time is hazardous, there is inadequate information as to what levels of radiation are safe over a long term of exposure. Typically, industry standards have set five REM per year as the maximum exposure to which a human should be subjected. A REM is a Roengten Equivalent Man, a well known measure of exposure to radiaion.
The radiation arises from the emission of alpha and beta particles as well as the emission of gamma rays. The beta particles and gamma rays present more of a hazard from external exposure than the alpha particles. This is because the alpha particles which comprise helium nuclei are charged and have a relatively high mass. Consequently, they can be stopped by a material such as a sheet of paper.
Beta particles, which are free electrons, have substantially greater penetrating power than alpha particles. Nevertheless, they can be stopped by a few millimeters of a metal such as aluminum.
Gamma rays, however, have unlimited range since they have the ability to make deep penetrations of material. They can only be minimized by a substantial thickness of a material such as lead.
As nuclear facilities tend to proliferate, the disposition of waste has become an increasing problem. This is because burial sites are at a premium and because huge quantities of waste are generated by these facilities. Waste which is highly active, such as spent nuclear fuel or the like, is buried after being placed in shielded canisters. However, because of the difficulty of obtaining burial sites, it is worthwhile to examine waste having a low activity to remove the nonactive components. This reduces the quantity of material which must be buried. Typically, waste having low activity includes paper, fabrics, boots, clothing, tools and various miscellany which can normally be expected to be used and disposed of in the operation of a nuclear facility. The waste may be collected in bags at the facility. It may include items that emit alpha and beta particles as well as gamma rays. Other items may not be radioactive. Occasionally, an effort may be made to sort items of high value such as tools and the like. However, this effort is usually discouraged because of the risk of personnel of radiation contamination.
As a result, large quantities of waste are generated for burial because they are believed to have low levels of radioactivity notwithstanding the fact that they have no radioactive content or that the materials which are radioactive can be readily segregated from the non-active waste. Consequently, much more material is being buried than is necessary.
The present invention relates to a method for segregating the components of radioactive waste having an activity above predetermined levels from the remainder of the waste. The method results in a substantial reduction in the volume of radioactively contaminated waste that need be buried.
The method is operable on an almost continuous basis. Further, it relys on detectors which generate alarms when radioactivity above predetermined levels is detected. It is especially advantageous since it can be operated by persons of relatively low skill.
Further, in the event of mechanical failure, those portions of the system which are operative can continue to operate while replacement parts are obtained for those portions which have failed.